If you use Powershell to delete the user, the user account isn't permanently deleted and will only get permanently deleted after 30 days have passed. There isn't a Powershell option for immediate permanent deletion. https://learn.microsoft.com/en-us/microsoft-365/enterprise/delete-and-restore-user-accounts-with-microsoft-365-powershell?view=o365-worldwide
To permanently delete the user, you need to go to the Microsoft Entra admin center and sign in as a User Administrator > go to Identity > Users > Deleted users > select Delete permanently. https://learn.microsoft.com/en-us/azure/active-directory/fundamentals/users-restore
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